Anti-static footwear

ABSTRACT

Anti-static footwear, having a member of substantially constant resistance conductively connecting the lower surface of the insole with an exposed face of the outer sole, wherein the resistance of the path between the foot of a wearer and ground remains substantially between a required upper limit and a required lower limit even if the insole should in use become a perfect conductor.

United States Patent Dalton 1 1 Aug. 5, 1975 [54] ANTI-STATIC FOOTWEAR2,818,534 12/1957 Horne 317/2 B 7 v 5] In e John A hur a on, A ma ale,3,293,494 l../1966 Fischer 317/2 B Australia [73] Assignee: Stat-E-ConPty. Limited, Prmwry Emmmer Hix v Melbourne Australia Attorney, Agent,or Fzrm-Depao1i & O Brien [22] Filed: Dec. 12, 1973 12 1 pp 423,991 57ABSTRACT [30] Foreign Application Priority Anti-static footwear, havinga member of substantially D 12 1977 NW 2e, nd 169 311 constantresistance conductively connectmg the lower surface of the insole withan exposed face of the outer sole, wherein the resistance of the pathbetween the 2? 3 1 47 foot of a wearer and ground remains substantiallybe- 1 B tween a required upper limit and a required lower 1 0 earc limiteven if the insole should in use become a perfect [56] References Citedconductor' UNITED STATES PATENTS 5 Claims, 2 Drawing Figures 2,712.0996/1955 Legge 317/2 B ANTI-STATIC FOOTWEAR This invention relates tofootwear (referred to generically herein as shoes) including shoeshaving outer soles of rubber, polyvinyl chloride or other thermallyand/or electrically insulating material.

In the past it has been found that some shoes became uncomfortable towear after a certain time during which they are in continuous orsubstantially continuous use by the wearer without him resting orremoving the shoes. This discomfort has been ascribed to various causesincluding increase in temperature of the feet and/or an accumulation ofstatic electricity in his body. Such a thermal or electrical chargecannot under normal walking conditions readily escape unless it bethrough his feet to the ground, and it will be evident that insulatingsoles such as of plastics tend to block any flow of electrical orthermal current from the body of the wearer.

It has been proposed to alleviate these shortcomings by rendering theoutersole conductive such as by forming it of graphite. However graphitehas not found favour because of its propensity to leave unsightly markson the floor or other surface upon which the wearer walks. In an attemptto overcome this problem it has been proposed to impregnate an otherwiseinsulating sole e.g. of rubber or plastics with metal or otherconductive particles or threads; but in the former case it is difficultto ensure sufficient interparticle contact to increase the conductivityof the sole to any significant extent. In the case of threads, theconductivity is liable to become excessive, because it needs but onethread to extend throughout the full breadth of the insulating materialto render the sole virtually a perfect conductor, especially if thatthread happens to be in the heel or ball portion of the foot where thecontact pressure with the ground is relatively high.

To have an excessively conductive path between the wearers body and theground can under some circumstances be undesirable because it exposeshim to the danger of electric shock should he happen to touch a sourceof high voltage.

I have found that one of the main sources of difficulty stems from theinsole. Most insoles are of leather or of a fibrous material which undernormal conditions is a reasonably good insulator. After a period of use,however, it tends to absorb perspiration from the foot whereupon itsresistance drops markedly e.g. from about 2 X 10 ohm to about 1 X 10ohm. Should the outersole have been rendered conductive (by means knownper se) i.e. usually having a resistance less than 2 X ohm, it will beevident that after a period of wearing, especially in warm weather,there will be a highly conductive path between the wearers body and theground. This could be dangerous if the wearer were exposed to highvoltage equipment.

It is an object of my invention to provide for controlling theresistance of this path between an upper limit of effectiveness orcomfort and a lower limit of safety, in a manner that is simple,relatively inexpensive and readily adaptable, to existing methods ofmaking footwear in general and soles in particular.

According to one aspect, the present invention provides footwearcomprising an outer sole or electrically insulating material and aninsole the resistance of which is liable to drop substantially uponabsorption of moisture from the wearers foot, characterized by theprovision between the insole and outer sole of a member of substantiallyconstant'resistance which conductively corrects the lower surface of theinsole with an exposed face of the outer sole such that when the wearerstands upon the ground, the resistance of the total electrical pathbetween his foot within the shoe and the ground contacted by saidexposed outer sole face, remains substantially between a required upperlimit and a required lower limit as hereinafter defined even if theinsole should in use become a perfect conductor.

The invention according to another aspect provides a method of makinganti-static footwear which comprises placing pre-manufactured conductivemembers into a mould for outer soles and then moulding the outer solearound the conductive members, but in order that the invention may bebetter understood reference will now be made to the accompanyingdrawings which are to be considered as part of thisspecification andread therewith. v I

In the drawings:

FIG. 1 is a section through part of a shoe according to one embodimentof this invention, and

FIG. 2 shows the lower exposed face of the of the shoe illustrated inFIG. 1.

Referring to the drawings in more detail, a shoe 3 has an electricallyinsulating outer sole 4 of rubber, polyvinychloride or otherelectrically insulating material and an insole 5 of fibrous or othermaterial and preferably cellulosic material rather than leather whichdeteriorates rapidly in such conditions because of heat, moisture,perspiration, etc. of which the electrical resistance is liable to dropsubstantially upon absorption of moisture from the wearers foot.

Between the insole 5 and outer sole 4 if a panel 6 of graphite rubber orother material of known resistance or at least of a resistance thatremains substantially constant under such conditions of use as will beexperienced by the shoe. Panel 6 is associated with the lower face ofthe insole i.e. the face which is lowermost in use, and is thinner thanthe outer sole so that no part of the panel extends to or beyond exposedface 7 of outer sole 4. Conductive means are provided so as electricallyto connect panel 6 with both the insole and exposed face 7 of outer sole4, so that when the wearer stands upon the ground, the resistance of thetotal electrical path between his foot within the shoe, and the groundcontacted by face 7, remains substantially within required limits, evenif the insole 5 should in use become a perfect conductor of electricity.

The conductive means between the panel and insole may include aconnection e.g. by means of graphite glue between these integers.

As shown in FIGS. 1 and 2 the conductive means between the panel andground may consist of a piece of fine wire mesh 8 fastened e.g. bystitching to the panel. Outer sole 4 may be moulded over the assembly ofinsole 5, panel 6 and mesh 8, but before doing so the ends of one seriesof wires making up the mesh are preferably interwoven into mutualcontact to ensure that at least some of the wires have ends 9 exposed inthe outer face 7 of the completed outer sole 4, as shownin FIG. 2.

Panel 6 and mesh 8 are advantageously attached to insole 5 in the regionof the ball of the foot, where the contact pressure with the ground isrelatively high. The electrical path may be considered to consist of theouter sole thickness of insole 5, that of panel 6 and finally thatprovided by metallic mesh 8. Since the resistance of the last mentionedis practically zero, the effective resistance of the electrical pathmust be regarded as that produced by the series arrangement of insoleand panel 6. As stated above, the resistance of the insole can varywidely depending inter alia upon the amount of moisture it may haveabsorbed. However as the resistance of the panel remains substantiallyconstant irrespective of resistance changes of the insole, the totaleffective resistance of the shoe can be predicted fairly accurately byvirtue of the insertion of the panel.

An advantage of this shoe resides in the fact that as the outsole wears,the thin metallic fibres the ends of which are exposed in the outersurface thereof wear at the same or substantially the same rate therebyreducing any tendency to scratch the floor or any other surface uponwhich the wearer walks. Those fibres may be of any suitable materialsuch as aluminum or copper, however the former is preferred as it doesnot tend to colour the outersole through chemical reaction.

The resistance panel may be attached to the insole by a surface"attachment which desirably may be conductive in nature e.g. a conductiveglue such as graphite glue which can be regarded as a conventional glueincorporating a suspension of graphite particles. Alternatively oradditionally, the attachment may be by means of tacks or spikes ofplastics or other material of low conductivity.

It will be evident from the foregoing that this shoe provides forcontrolling the conductivity of footwear between close limits,irrespective of substantial resistance changes in the insole, in amanner that is simple, inexpensive and readily amenable to conventionalmethods used in the boot trade.

This shoe also finds advantageous application in operating theatreswhere it is highly desirable that staff should wear shoes that aresufficiently conductive to avoid build up of body static electricitywhich might lead to sparking, but of sufficient resistance to minimisethe likelihood of fatal shock in the event of the wearer coming incontact with high voltage e.g. X-ray apparatus or electromedicalequipment.

For similar reasons this shoe can be worn to advantage in chemicallaboratories and plants or installations where explosive substances aremanufactured or volatile substances handled.

It is pointed out that most conductors of electricity are alsoconductors of heat and therefore the anti-static footwear according tothe present invention can also be used such that they are not only beingused to dissipate heat.

Some applications of this use are those of sporting shoes, such as golfshoes, bowling shoes and the like.

Thus the present invention provides novel anti-static footwear thatfulfills all requirements yet has the additional features that it issafe to use near high voltage equipment, easily manufactured, relativelyinexpensive, will not mark floors and can be made in many varyingstyles.

What I claim is:

1. Anti-static footwear having an electrically insulating outer sole andan insole the resistance of which is liable to drop substantially uponabsorption of moisture from the wearers foot, comprising a member ofsubstantially constant resistance which conductively connects the lowersurface of said insole with an exposed face of said outer sole such thatwhen a wearer of said anti-static footwear stands upon the ground, theresistance of the total electrical path, between his foot within saidfootwear and said ground contacted by said exposed face of said outersole, remains substantially between a required upper limit and arequired lower limit, even if said insole should in use become a perfectconductor, said member comprising:

A. a panel which contacts said lower surface of said insole and isthinner than said outer sole so that no part of said panel extends to orbeyond said exposed face of said outer sole, and

B. a conductive means which electrically connects said panel with saidexposed face of said outer sole.

2. The footwear of claim 1 wherein said panel extends over a smallerarea than the area of said insole and said outer sole.

3. The footwear of claim 2 wherein said panel is located in the vicinityof the ball of said foot.

4. The footwear of claim 1 wherein said conductive means comprises metalthreads in electrical communication with said panel and having at leastone end extending to said exposed face of said outer sole.

5. The footwear of claim 4 wherein said metal threads are at least partof a piece of fine wire mesh.

1. Anti-static footwear having an electrically insulating outer sole andan insole the resistance of which is liable to drop substantially uponabsorption of moisture from the wearer''s foot, comprising a member ofsubstantially constant resistance which conductively connects the lowersurface of said insole with an exposed face of said outer sole such thatwhen a wearer of said anti-static footwear stands upon the ground, theresistance of the total electrical path, between his foot within saidfootwear and said ground contacted by said exposed face of said outersole, remains substantially between a required upper limit and arequired lower limit, even if said insole should in use become a perfectconductor, said member comprising: A. a panel which contacts said lowersurface of said insole and is thinner than said outer sole so that nopart of said panel extends to or beyond said exposed face of said outersole, and B. a conductive means which electrically connects said panelwith said exposed face of said outer sole.
 2. The footwear of claim 1wherein said panel extends over a smaller area than the area of saidinsole and said outer sole.
 3. The footwear of claim 2 whereiN saidpanel is located in the vicinity of the ball of said foot.
 4. Thefootwear of claim 1 wherein said conductive means comprises metalthreads in electrical communication with said panel and having at leastone end extending to said exposed face of said outer sole.
 5. Thefootwear of claim 4 wherein said metal threads are at least part of apiece of fine wire mesh.